The last decade has witnessed the emergence of a new frontier in the manufacturing technology, commonly referred to as solid freeform fabrication (SFF) or layer manufacturing (LM). A LM process typically involves representing a 3-D object with a computer-aided design (CAD) geometry file. The file is then converted to a machine control command and tool path file that serves to drive and control a part-building tool (e.g., an extrusion head) for building parts essentially point by point and layer by layer. The LM processes were developed primarily for making models, molds and dies, and prototype parts for industry uses. They are capable of producing a freeform solid object directly from a CAD model without part-specific tooling or human intervention. A SFF process also has potential as a cost-effective production process if the number of parts needed at a given time is relatively small. Use of SFF could reduce tool-making time and cost, and provide the opportunity to modify tool design without incurring high costs and lengthy time delays. A SFF process can be used to fabricate certain parts with a complex geometry which otherwise could not be practically made by traditional fabrication approaches such as machining.
Examples of SFF techniques include stereo lithography (SLa), selective laser sintering (SLS), 3-D printing (3-DP), inkjet printing, laminated object manufacturing (LOM), fused deposition modeling (FDM), laser-assisted welding or cladding, shape deposition modeling (SDM), to name a few. There are several shortcomings associated with these SFF techniques. In most of these techniques, for instance, the fabrication of a 3-D object either requires the utilization of expensive and difficult-to-handle materials or depends upon the operation of heavy, complex and expensive processing equipment. For example, the photo-curable epoxy resin used in the stereo lithography process can cost up to US$300 per pound. Melting of metallic, ceramic, and glass materials involves a high temperature and could require expensive heating means such as an induction generator or a laser. Thermoplastics also require a moderately high temperature (normally in the range of 140.degree. C. to 380.degree. C.) to reach a low-viscosity state for processing. Most importantly, most of these prior-art techniques can not be used to fabricate edible food items like cakes. All these layer manufacturing techniques require that, in a layer-additive fabrication process, a layer be solidified to become a solid before another layer is built. Most of these prior-art LM techniques are not capable of fabricating multi-material or multi-color objects.
Other shortcomings of the prior-art SFF techniques are briefly summarized as follows: The FDM process (e.g., U.S. Pat. No. 5,121,329; 1992 to S. S. Crump) operates by employing a heated nozzle to melt and extrude out a material such as nylon, ABS plastic (acrylonitrile-butadiene-styrene) and wax. The build material is supplied into the nozzle in the form of a rod or filament. The filament or rod is introduced into a channel of a nozzle inside which the rod/filament is driven by a motor and associated rollers to move like a piston. The front end, near a nozzle tip, of this piston is heated to become melted; the rear end or solid portion of this piston pushes the melted portion forward to exit through the nozzle tip. The nozzle is translated under the control of a computer system in accordance with previously sliced CAD data to trace out a 3-D object point by point and layer by layer. This process has a drawback that it requires a separate apparatus to pre-shape a build material into a precisely dimensioned rod or filament form. The re-melting of this rod or filament in a FDM nozzle requires additional heating elements placed around or inside the body of the nozzle. Furthermore, this process obviously is not capable of fabricating food objects.
Additional FDM-type processes can be found in U.S. Pat. No. 5,503,785 (Apr. 2, 1996) issued to Crump, et al., U.S. Pat. No. 5,866,058 (Feb. 2, 1999) to Batchelder and Crump, U.S. Pat. No. 5,939,008 (Aug. 17, 1999) to Corn, et al., U.S. Pat. No. 5,968,561 (Oct. 19, 1999) to Batchelder, et al., U.S. Pat. No. 5,340,433 (Aug. 23, 1994) to Crump, U.S. Pat. No. 5,738,817 (Apr. 14, 1998) to Danforth, et al., and U.S. Pat. No. 5,900,207 (May 4, 1999) to Danforth, et al. In these latter two patents, a FDM process is disclosed to fabricate a ceramic object from a mixture of ceramic particles dispersed in a binder. The mixture is made into a filament or rod form which is fed into a nozzle in which the binder is melted to make the mixture in a fluent paste state. Upon discharge from the nozzle, the binder is solidified to hold the ceramic powder in a desired shape (in which all ingredients are now solids). The binder is later burned off and the remaining ceramic "green" body is subjected to a high temperature sintering treatment to produce a useful ceramic article.
A particularly useful SFF technique is based on extrusion of heat-meltable materials or thermoplastics. In principle, a bulk quantity of materials (thermoplastics and wax) can be melted and directly transferred to a dispensing nozzle for deposition; it does not require the preparation of a raw material to a special shape followed by re-melting. One example of an extrusion-type (but not based on the LM or SFF approach) is given in U.S. Pat. No. 4,749,347 (Jun. 7, 1988) issued to Valavaara. Extrusion-based SFF processes can be found in U.S. Pat. No. 5,141,680 (Aug. 25, 1992) to Almquist and Smalley, U.S. Pat. No. 5,303,141 (Apr. 12, 1994) and 5,402,351 (Mar. 28, 1995) both to Batchelder, et al., and U.S. Pat. No. 5,656,230 (Aug. 12, 1997) to Khoshevis. In these examples, the starting material is heated to become a melt and then transferred to a dispensing head by using a gear pump, a positive-displacement valve, an air-operated valve, or an extruder. The nozzle also must be heated to maintain the material in the molten state prior to being extruded out for deposition.
Examples of extrusion-based SFF techniques using thermosetting resins are given in U.S. Pat. No. 5,134,569 (Jul. 28, 1992) to Masters and U.S. Pat. No. 5,204,124 (Apr. 20, 1993) to Secretan and Bayless. Both systems require the use of an ultra-violet (UV) beam or other high energy sources to rapidly cure a thermosetting resin. Photo-curable or fast heat-curable resins are known to be expensive and the curing processes have very limited processing windows; curing of these materials has been inconsistent and difficult and the results have not been very repeatable. Obviously, one would not use a thermosetting resin for making a cake.
An extrusion-based SFF process requires the extruded material quickly solidify to become a solid so that it can support its own weight and other layers that are subsequently deposited thereon without experiencing a significant deformation or shape change. This condition can be readily met with heat-meltable or thermoplastic materials by rapidly cooling the dispensed materials below their melting points. In the present invention, a food composition used in an extrusion type SFF process remains in an essentially non-solid state (e.g., a cake mix or other food paste). The food composition in a layer does not need to become a solid before a subsequent layer is deposited onto this layer. The only requirement imposed on the physical state of the food composition of a layer is that it has sufficient rigidity and strength to support its own weight and the weight of subsequent layers. The process does not require either a high energy source (like in the case of UV-curable resins) to achieve a solidification state, or a great amount of heat energy to melt the material and then a cooling means to help solidify the material (like in the case of thermoplastics). Instead, the food material composition is formulated to contain a liquid ingredient (such as water) which acts to make the food composition in a fluent state to facilitate dispensing from a nozzle. This liquid ingredient does not have to be removed during the object-building procedure. Because there is no need to solidify individual layers before subsequent layers are deposited, solidification of these layers would not become a constraining factor in limiting the speed of object fabrication. This is in contrast to essentially all conventional freeform fabrication processes in which individual layers must be solidified prior to deposition of a subsequent layer. The presently invented freeform fabrication method can be used to make a brilliant 3-D decorative icing/topping shape on a baked cake. The method may also be used to form a cake mix into a desirable shape before being baked in a oven; in this case, the final shape could be different from the original shape.